Double-frequency resonant choke coil



Oct. 21, 1941. J, BROWN ET AL 2,260,164

DOUBLE-FREQUENCY RESONANT CHOKE COIL Filed Jan. 24, 1940 5 INVENTORS Myra/1 LIB/"own and fzr'a 7? Hughes.

ATTOR N EY Patented Oct. 21, 1941 UNITED STATES PATENT OFFICE, j;

2,260,164 DOUBLE-FREQUENEAIRKESONANT CHOKE Myron J. Brown and Ezra T. Hughes, Wilkinsburg,Pa., assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 24, 1940, Serial no. 315,384

4 Claims.

Our invention relates to resonant carrier-current line-connected choke-coils, and it has particular relation to novel means for obtaining parallel resonance to two difi'erent adjustable carrier-current frequencies in a manner which will admit of a satisfactory mechanical construction, with small-sized capacitors, in a low-resistance circuit (so-that the tuning'is sharp), and with facilities for easy adjustment of the two carriercurrent frequencies in the field.

The principal object of our invention is to provide a new circuit for converting asingle-frequency resonant choke-coil, having facilities for adjusting the frequency of resonance, into a trating also the conversion from a single-frequency resonant choke-coil to a double-frequency choke-coil;

i Fig. 3 is a curve-diagram which is referredto in the explanation of the diagram shown inFig,

2 and i Fig. 4 is an equivalent-circuit diagram illustrating the benefit of a transformer for connect ing the tuning capacitor-of the second tuning unit. a k

Our invention is particularly adapted-tothedesign of a carrier-current resonant line choke-coil such as is adapted to be connected in circuitwith one of the line-conductors of a-transmission-line on which are superimposed carrier-currents of twodifierent frequencies, the object being to tune the line choke-coil to parallel resonance to the two carrier-current frequencies so that the chokecoil will block, or strongly impede, thefiow of currents of both of the carrier frequencies. The carrier-currents may be utilized, on the transmission system, either for protective relaying, or communication, or remote control.

Our invention is particularly designed for use in combination with a relatively heavy-current line-connected chokemoil of a type in which a. 55 be made, as indicated atandlll, j I t stranded flexible cable or conductor 5 is wound about an insulatingtubular support 6,..whichmay be of porcelain, to constitute the main inductance L1, as shown in Fig.1, Whenthis type of flexiblecable inductance-coil L1 is utilized, it is not pracf ticable to tap on adjustable taps at adjustable, points,.in the field, because ofthe diificulty of making connections to the sides, of the coils at intermediate points. Itis afeature o f 'our,present invention, therefore, to. make all of ,the vconnec; tions to the terminals of the main coil L1, atv the points where said coil is connected in series with the line-conductor 8. p H

The line-connected with is commonly protected against excess-voltage surges by means of alightning arrester which is illustratedas com-' prising a valve-typeelement lllandaseriesgao I l the lightning arrester, l0.- l Ibeing connected between the terminal line-connectionsfi ii, and being mounted somewhere within, orup onthe structure of, the main line-coil L1, usually at one of the ends thereof. It has also been customary to connect the tuning equipmentacrossthejt'erminals l2-l3 of the lightningarrester ill-ll, the connection being made at points close to said terminals, so as to avoid the voltage-drop which is encountered in the. relatively long conductor U! which runs inside of the line-connectedcoilLrto make connectionto the line-terminal 8 at theend opposite to the end at which the lightning ar-' rester I0ll is mounted; and we have indicated such connections at l5 and [6,, 3 H

In accordance with ourinvention, we, utilize two relatively light-current. tuning-units, which are indicated in their, entirety by the numerals ,l l and [8, respectively, said units being suitably mounted Within the line-coil L1 by'mechanical supporting meanswhich do not constituteapart of our, present invention. The tuning-unit l1 consists essentially of a capacitor C1 and avariometer L2, while the tuning unit 18 consists es;

although we are not necessarily limited to this particular type oftu'ning-unit. I Inthe particular form illustratedin l fig, 1 each of the capacitors Cl and Czis split up, into ,four separatecapacitors 2 I, 22, 2'3 and 2 4,,the terminals of which are connected to binding posts ZSLon .a terminalboard to which various connections can an ce Ls shounted by a capacitance C2.

readily apparent that various combinations of capacitive impedances are represented asminus series, parallel and series-parallel capacitors may j be chosen in order to effect tuning to any desired frequency within the range of the apparatus.

The variometer L2 of the first tuning-unit I1 is essentially merely a Vernier adjustment-means for effecting continuous tuning between the steps which are provided-by the different combinations of series, parallel,-and series-parallel capacitors:

"These two impedances are resonant at the freof the capacitance-group 2 l- -24 which comprises the capacitor C1; and in the equivalent diagrami of Fig. 2, the group C1-L2 is represented simply is connected in shunt to the capacitance C2, so as the second tuning-unit I8 quantities, as y'X.

In Fig. 3, the impedance of the line-coil L1 is indicated at XL being equal to 21rfL1. The impedance of the equivalent capacitance C1 of the first tuning-unit I] is indicated at Xc being equal to quency marked ii. The impedance'of the parallel-connected inductance L3 and capacitance "C2 of .the second tuning-unit I8 is indicated at to provide a parallel-resonant circuit which is I connected in series with the capacitance Ci, the" unit l8, as indicated by the full-line position of the switch 30 in Fig.2.

The actual connections, as illustrated in Fig. 1, may be traced from the right-hand line-terminal 8, through v the conductor l4 and'the junctionpoint IE, to th'evariometer Lz'a'nd thence to the capacitor 01, after which the circuit is extended, through a conductor 32, to the terminal 33 of the secondtuning-unit l8. At the point 33,'the circuit divides, one part passing through the portion 34-35 of the variometer L3, as shown in Fig. 1, and thence extending on, through alconductor 36, to the junction-point l6 and the lefthand line-terminal 8. This portion 34-35 of the variometer L3 is represented by the inductance L; in .the equivalent-circuit diagram of Fig.

terminal .33 'of the. second tuning-unit l8 includes the capacitor C2 whichis connected. across nearly all of thevariometer L3, or from the terminal 34 'to' the terminal 31, as shown in Fig. 1. In this respect, the variometer L3 of Fig. 1 operates as a step-up transformer which increases the voltage on the capacitor C2, as indicated by the. mutual impedance M3, or two-winding transformer .Msfwhich is shownin the equivalent diagramof Fig. 4. The capacitor C2 is thus con: nected in-parallel-circuit relation to the variouseter-portion 34-35 which is connected in circuit l5, so "that, disregarding the transformation ratios, the equivalent-circuit diagram of Fig. 2 represent s ;.the connection simply as an induct:

entire series being connected across the line 7 though this is by no means requisite.

' X L c in Fig. 3, this impedance being inductive, for frequencies below the resonant-frequency I of the combination L3, C2, as indicated by the curve 40 in Fig. 3, and being capacitive at higher frequencies, as indicated by the curve 4| in Fig. 3. The algebraic sum of the parallel-circuit impedance 40 or 4| and the impedance Xc of the capacitance C1 of the first tuning-unit 11 is also plotted, in Fig. 3, as the curves 42 and 43, respec- 7 tively; and it will be noted that these impedances 42 and 43 are resonant with the line choke-coil impedance *XLI at the frequencies fa and f3, respectively. The entire resonant choke-coil com 'bination thus presents a condition of parallel resonance at each of the two carrier-current fre-' quencies fzand is," it being noted that the afore-' said frequencies in and f1 are intermediate frequencies, which may, or may not, be coincident with each other. It is generally convenient to make the intermediate frequenciesfo and ii at approximately the same order of magnitude, al-

In actual practice, various combinations of the I terminal-board connections 25, 2'6 and 2 1 (Fig.

T e other circuit whichis traceable from the between thefterminal 33 and the junction-point Theoperation of the circuit shown in 2 is illustrated by the impedance-diagrams of Fig.

a ing represented as positive values, as +y'X, while 1) ,forthe respective tuning-units l1 and I8, are selected at the factory, and tabulated for use, in the field, when the customer desires to'tune the choke-coil to' different desired carrier-current frequencies f2 and is, with the result that r the operator or lineman, by choosing the proper com bination of capacitors, and by properly adjust ing the variometers It: and L3, can quickly and easily effect any desired tuning, to any desired frequency, over'an extremely wide range.

Although it is not readily apparent on a'surface-examination, our novel I tuning-system, as hereinabovedescribed, is extremely economical, in requiring relatively small (and hence relatively inexpensive) capacitors, at the same time providing an extremely simple method of tuning.

Our utilization of the second variometer'Ie as" a transformer, is also useful becauseit reduces the number of turns of the variometer which have to be connected in series in the circuit 33-46 in order to effect the tuning, thus reducing the ratio of resistance to reactance in the circuit. Experience-has also'shown that this expedient also equalizes the magnitudes of the peaks of the inipedanceat the two critical frequencies of our doubly tuned reactance-device. Thereduced-resistance efifect may be perceived by a comparison of the equivalent diagrams which are shown in Figs. 2 and 4, respectively. In Fig. 2, it may be re'g'arded, for the moment; that the whole variometer L3 is connected in the circuit 33 I6 in order to provide as mu'ch'in ductance as possible, so as to reduce the required sizeof the parallel-resonant capacitor C2} but even with this precaution the equivalent capacitor C2 is relatively large. In Fig. 4, the primary of the mutual coupling-device M3 comprises only a few turns, corresponding to the variometer-portion 34-35 of Fig. 1, and the voltage of the capacitor C2 is stepped up by means of a transformer secondary-winding 41 of many turns, so that a small, high-voltage capacitor C2 may be utilized, thus making the design less expensive, and requiring a smaller space for the equipment which is included in the second tuning-unit 18. At the same time, the small number of turns of the primary winding of the mutual coupling-device M3 in Fig. 4, means that a relatively small resistance is connected in the circuit 33-16, a few turns having a smaller resistance than many turns, thus keeping the peak-impedances of the parallelresonant line choke-coil all sharply tuned.

While we have illustrated our invention in a preferred form of embodiment, and while We have described the same in accordance with our best theory of understanding of the same, we do not wish to be strictly limited thereto, as various changes may be made by those skilled in the art, without altering the essential principles of our invention, particularly in its broader aspects. We desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language and the prior art.

We claim as our invention:

1. The combination, with a relatively heavycurrent, large-diameter line-connected chokecoil, of relatively light-current tuning-means disposed within said line-connected-choke-coil for tuning said line-connected choke-coil in parallel resonance to at least two carrier-current frequencies, said tuning-means comprising a first variable capacitive impedan-ce-device, a parallel-resonant group comprising a variable inductive impedance-device and a second variable capacitive impedance-device in parallel-circuit relation to each other, and connections for connecting said first variable capacitive impedance-device and said parallel-resonant group in series with each other, and across said line-connected choke-coil, whereby the entire choke-coil combination is tuned to two frequencies, one above, and one below, both the resonant frequency of said parallel-resonant group and the resonant frequency of said line-connected choke-coil and said first variable capacitive impedance-device.

2. The invention as defined in claim 1, characterized by said variable inductive impedancedevice being a transformer-means connected to the terminals of said second variable capacitive impedance-device for stepping up the voltage applied to said second variable capacitive impedance-device and reducing the ratio of resistance to reactance in said variable inductive impedance-device.

3. The combination, with a relatively heavycurrent, large-diameter line-connected chokecoil, of relatively light-current tuning-means disposed within said line-connected choke-coil for tuning said line-connected choke-coil in parallel resonance to at least two carrier-current frequencies, said tuning-means comprising a first variable capacitive impedance-device, a parallelresonant group comprising an auxiliary inductive impedance-device and an auxiliary capacitive impedance-device in parallel-circuit relation to each other, means for varying at least one of the auxiliary impedance-devices comprising said parallel-resonant group, and connections for connecting said first variable capacitive impedancedevice and said parallel-resonant group in series with each other, and across said line-connected choke-coil, whereby the entire choke-coil combination is tuned to two frequencies, one above, and one below, both the resonant frequency of said parallel-resonant group and the resonant frequency of said line-connected choke-coil and said first variable capacitive impedance-device.

4. The invention as defined in claim 3, characterized by said auxiliary inductive impedancedevice being a transformer-means connected to the terminals of said auxiliary variable capacitive impedance-device for stepping up the voltage applied to said auxiliary variable capacitive impedance-device and reducing the ratio of resistance to reactance in said variable inductive impedance device.

MYRON J. BROWN.

EZRA T. HUGHES. 

